This invention relates to wheel balancers and in particular to improved wheel balancers with improved measurement capabilities.
The determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by imbalance and noise.
Even when a wheel/tire assembly is balanced, non-uniformity in the construction of the tire as well as runout in the rim can cause significant vibration forces as the wheel rolls under vehicle load. Most tire manufacturers inspect their tires on tire uniformity machines and grind rubber off the tires as required to improve rolling characteristics of the tires. Even after this procedure, tires will often produce vibration forces (not related to imbalance) of 20 pounds as they roll on a smooth road. To put this in perspective of balancing, a 0.8 ounce balance weight is required to produce a 20 pound vibration force on a typical wheel traveling at 70 mph.
Many conventional balancers also assume that the wheel/tire assembly which is suitably balanced under an essentially no-load condition will also be suitably balanced when installed on the vehicle and subjected to the substantial load represented by the weight of the vehicle. This assumption is not valid under all conditions. It would be preferable in many circumstances to simulate loaded conditions to improve the results of the balancing operation.